This invention relates to fuel-cell systems, and in particular, to the replacement of fuel stacks in fuel-cell systems.
A fuel cell converts chemical energy to electrical energy by promoting a chemical reaction between two reactants. In a typical fuel cell, a hydrogen source is placed in contact with one side of a membrane and an oxygen source is placed on the other side of the membrane. The membrane is selected to be permeable to protons but not to electrons. A catalyst, such as platinum, coats the membrane and facilitates the passage of protons across it.
In operation, hydrogen atoms on one side of the membrane decompose into protons and electrons. The protons pass through the membrane but the electrons cannot. This results in the formation of a modest electrical potential across the membrane. To provide a system with increased voltage and higher output, a number of these fuel cells may be connected in series. The resulting structure, in which the membranes appear to be stacked one on top of the other, is referred to as a xe2x80x9cstack.xe2x80x9d
To generate power, the stack must be provided with a flow of reactants, or fuel. In addition, heat generated by the reaction may be removed by a coolant to maintain a desired temperature. The fuel may be provided by, for example, a fuel processor that converts a hydrocarbon (such as natural gas or methanol) into a hydrogen-rich reformate. Inlet and outlet streams for air, fuel and coolant are plumbed to the stack.
A typical stack can be heavy and unwieldy, making installation and removal for service difficult. For example, a 7 kW stack assembly containing eighty fuel cells using carbon composite flow field plates may weigh more than one hundred pounds. During installation, it may be necessary to place such a stack in a confined space within the fuel cell system while ensuring accurate placement. Some fuel-cell systems may include a manifold base that a stack can be plugged into or aligned with to simplify plumbing connections to the stack. An example of such a fuel-cell system is described in U.S. patent Ser. No. 09/703,082, entitled xe2x80x9cFuel Cell Coolant Tank Systemxe2x80x9d filed on Oct. 31, 2000 and assigned to Plug Power Inc., the contents of which are hereby incorporated by reference in their entirety. In such systems, accurate placement of the stack during installation can be critical, for example to align and seal the fluid connection apertures of the stack with the fluid connection apertures of the base.
The invention provides a hinge that couples a fuel-cell stack to a base. In some embodiments, the hinge enables a field service technician to pivot the stack onto the base so that a stack-aperture on the stack mates with a base aperture on the base. However, in the context of the invention, the base can refer to any platform or position to which the stack is positioned or installed within the fuel-cell system, regardless of whether the base itself contains fluid connection apertures that mate to the stack.
In one aspect of the invention, a separable hinge includes a first hinge-element attached to a base of a fuel-cell system and a second hinge-element attached to the stack. Using the separable hinge, a field-service technician can mount the stack onto the base by aligning the first and second hinge-elements and then engaging them. Once the first and second hinge-elements are engaged, the hinge is complete and the stack can be pivoted about an axis defined by the hinge. The field service technician can then pivot the stack around this axis and into the correct position on the base.
A fuel-cell system incorporating the invention includes a fuel-cell stack having one or more stack-apertures and a base having one or more base-apertures to be mated with corresponding stack-apertures. A separable hinge attached to both the fuel-cell stack and to the base defines a pivot axis and enables the stack aperture to be pivoted about this pivot axis and into engagement with the base-aperture. The separable hinge defines a first position in which the stack and the base are inseparable and a second position in which the stack and the base are separable.
The separable hinge can include a first hinge-element and a second hinge-element. The second hinge-element is configured to engage the first hinge-element when the fuel-cell stack is at a first position relative to the base, and to disengage from the first hinge-element when the fuel-cell stack is at a second position relative to the base.
In one type of separable hinge, a transition between the first and second positions occurs as the stack is pivoted about the pivot axis. In this type of separable hinge, a pin on the first hinge-element defines the pivot axis. This pin is supported by one or more knuckles that are attached to either the stack or the base. The second hinge-element can then include a curled engagement portion for engaging the pin. The curled engagement portion follows an arc of a circle having a radius-of-curvature corresponding to a radius-of-curvature of the pin.
In another type of separable hinge, transition between first and second positions is effected by translating the stack relative to the base along a direction defined by the separable hinge. In one embodiment of this type of separable hinge, a pin mounted on the first hinge-element defines both a pivot axis and an axis of translation. In this embodiment, the second hinge-element can include a wall that forms a passageway for receiving the pin. The first and second hinge-elements can thus be brought into engagement by sliding the pin through the passageway. Conversely, the first and second hinge-elements can be separated by sliding the pin out of the passageway.
In yet another type of separable hinge, the first hinge-element defines a groove and the second hinge-element includes a spindle configured to be lifted into and out of engagement with the groove. When the spindle rests in the groove, the stack can be rotated into position over the base using a pivot axis defined by the groove.
By providing an axis about which the stack can be pivoted into position, the hinge eliminates the need to align the stack-apertures with the base-apertures. In effect, the task of aligning the stack apertures with the base apertures is replaced by the much easier task of aligning first and second hinge-elements. By supporting a portion of the stack""s weight at the time that the stack is being installed, the hinge avoids imposing the entire weight of the stack on a technician during installation, either in the factory or in the field.
As used herein, xe2x80x9chingexe2x80x9d refers to any structures or structural elements that collectively define an axis about which the stack can be pivoted into position on the base. The structures or structural elements included in a hinge can be attached to the base, attached to the stack, or both. Alternatively, the structures or structural elements included in the hinge can be integral with the base, integral with the stack, or integral with both the stack and the base.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. In case of conflict, the present specification, including definitions, will control.
Although methods and materials similar or equivalent to those described herein can be used in the practice or testing of the present invention, suitable methods and materials are described below. In addition, the materials, methods, and examples are illustrative only and not intended to be limiting.
These and other features of the invention will be apparent upon examination of the following detailed description, the claims, and the figures, in which: